The present invention relates to variable compliance assemblies and more particularly to a variable compliance assembly for an automatic assembly operation utilizing a fluid spring for providing multi-directional compliance movement of a gripper member or similar device.
The uses of robots in the assembly of close-fitting mechanical parts has become widespread. The assembly of close-fitting mechanical parts, however, usually has predetermined tolerances between the workpiece and the receiving part. Compliance assemblies enable a workpiece to be inserted into a receiving part when the centerlines of the workpiece and the receiving part are not exactly collinear with one another to minimize assembly forces and the possibility of jamming or destruction of parts due to machining inaccuracy, parts variation, and fixturing tolerances.
Several compliance assemblies have attempted to resolve variation in centerlines between a workpiece and a receiving part. U.S. Pat. No. 4,276,697 (Drake and Simunovic) discloses a compliance assembly utilizing a multi-stranded cable having an elastomeric collar for providing compliance movement in the assembly. U.S. Pat. No. 4,155,169 (Drake and Simunovic) discloses a compliance assembly utilizing deformable members for providing compliance movement in the assembly. U.S. Pat. No. 4,098,001 (Watson) discloses a compliance assembly utilizing deflectable members for providing compliance movement in the assembly. Also, a technical paper entitled "Using Compliance In Assembly--An Engineering Approach To Float", CASA MS79-873, by Drake, Spencer, and Simunovic discloses compliance assemblies utilizing springs and elastomeric shear pads for providing compliance movement in the assembly.
The above-described assemblies, however, have several disadvantages. Springs, cables, deformable members, and deflectable members are subject to fatigue failure. The failure of these elements in turn causes the automatic assembly operation to be stopped for a repair period which, in turn, stops production. The above assemblies are also highly complicated, include several moving parts, and involve precision tooling in the manufacturing of the assemblies. The resilient elements are assembled on the compliance assemblies at very precise angles, making the compliance assemblies complicated and costly to manufacture.
The present invention overcomes the disadvantages of the prior art by providing a relatively simple and relatively inexpensive variable compliance assembly. The new and improved variable compliance device of the present invention includes a housing having an interior chamber and a base member positioned in the housing and seated on a surface of the interior chamber. Generally, the base member is secured to a gripper and provides the gripper with multi-directional compliance movement. The variable compliance assembly further comprises a fluid spring associated with the housing and the base member for providing the base member with multi-directional compliant movement to correct for lateral, out-of-square, or other misalignment, and for returning the base member to a normal, self-centering seating position. A passageway in the housing is also disclosed for transfer of pressurized fluid to and from the interior of the fluid spring to enable the fluid spring to have varying degrees of pressure and compliance.
Other objects and advantages of the present invention will become apparent to one skilled in the art in view of the following specification, accompanying drawing, and appended claims.